Monospecific antibodies, some already prepared, some still to be made using preparatory crossed immunoelectrophoresis, will be used to analyze bacterial coaggregation associated with dental plaque formation as a cause of peridontal disease. Monovalent Fab derivatives of these antibodies will be used to identify antigens responsible for coaggregation, locate these antigens in the bacterial anatomy, and help classify the bacteria participating in plaque-associated coaggregation. They will be used also with electron microscopy to identify the supposedly relevant bacteria in normal and disease-producing plaque.